Calender stack with swimming roll

ABSTRACT

The use of a stacked paper calender with a single stack of rolls in place of the usual tandem arrangement is promoted by providing an intermediate variable deflection roll and controlling the internal fluid pressure within the roll to control roll deflection under load in relieving or increasing the nip loads in the lower portion of the stack. The intermediate roll is supported by end bearings which are provided with control means for applying upward relief force.

United States Patent [56] References Cited [72] Inventors Rodney HaroldBryce Lachlne, Quebec;

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gle stack of rolls in place of the usual tandem arrangement is 100/162, promoted by providing an intermediate variable deflection roll and controlling the internal fluid pressure within the roll to control roll deflection under load in relieving or increasing 100/170 [51] Int. 1330b 3/04 [50] Field 100/155, the nip loads in the lower portion of the stack. The inter- 160, 161, 162 A, 164, 168, 170, 171, 176; 29/1 16 mediate roll is supported by end bearings which are provided with control means for applying upward relief force.

AD,113AD CALENDER STACK WITH SWIMMING ROLL This invention is directed to an improved calender stack.

in the operation of paper machines for manufacturing paper it is necessary to pass the formed paper web through a series of sequential pressure nips provided by calendering rolls in order to provide the desired finish and density of paper. Owing to the increases in speeds of modem paper machines, the roll diameters have also increased, to avoid running near the critical speed range of the individual rolls. This has resulted in the increase of roll weight to the point that a full roll stack produces crushing of the sheet. This has led to the practice of splitting the full stack, resulting in two separate stacks of calender rolls.

It will be seen that splitting of a full stack of up to eight rolls into two adjacent stacks produces substantial increases in direct cost and floor space requirement of the calender section of a paper machine.

When a loaded roll is supported by its ends, the roll deflects. in the case of a calender stack, deflection of the bottom roll results in an uneven loading of the paper web, with increased nip pressure at the edges. To overcome this, the bottom calender roll is often crowned, the amount of crown being calculated for the total load above.

Should an intermediate roll be lifted on its journals or load relieved" as taught in Canadian Pat. No. 322,670, Malkin, dated May 25, I932, this roll will require to be crowned, the amount of crown depending on the weight of the rolls above, and the relief load applied to the journals of the intermediate roll.

For constant calendering conditions such an expedient is effective. However, conditions are not generally constant, and it can be readily seen how impractical is the solution of adjusting the crowning of the intermediate roll, to suit changed working conditions, by regrinding the roll or substituting a different roll of differing crown.

A known, previous arrangement for improving calender stack arrangements, provided an antideflection roll having the supporting shafts of the roll joumaled inboard of the roll ends, at about the quarter-span positions, to improve the deflection characteristic of the roll.

it has been found that such rolls can only provide complete deflection relief when in an unloaded condition, but that inherent, residual deflection when in the loaded condition is sufficient to impede the satisfactory functioning of the arrangement in providing load relief to the lower rolls of the stack.

In the present invention, by substituting a nondeflecting roll such as a "swimming roll in an intermediate position of the stack, in load-relieving relation to the lower rolls, such that web crushing is avoided, it is possible to provide a full stack, while avoiding the need of crowning the intermediate roll.

Am alternative arrangement incorporates a controllable deflection intermediate roll, in which fluid pressure within the roll is varied, to control the deflection of the roll. This permits greater loading of the upper portion of the calender stack without overloading at the lower nips of the stack.

The present invention makes possible the provision of a full stack of high-speed calender rolls, having a large number of rolls, and including an intermediate roll of the nondeflecting or controlled deflection type provided with journal load adjustment means whereby the transference of nip loading from the series of rolls above the nondeflecting or controlled deflection roll to the series of rolls therebeneath may be selectively controlled.

By providing a nondeflecting or controlled deflection roll in an intermediate load relief position, untoward bowing of the conventional rolls due to the stack loading, both above and below the intermediate roll, is greatly diminished, the nip pressures may be readily regulated and improved control of paper quality is provided.

Owing to the wide range in varieties of paper, while it is generally desirable to relieve the lower rolls, of the stack of some portion of the weight of the upper rolls, in certain instances when very dense fine papers requiring high finishes are calendered it may prove desirable to increase the loading of the lower rolls by applying a downward force at the journals of the nondeflecting or controlled deflection roll, so urging the roll downward in a nip-loading fashion.

It will be seen that the present invention may be practiced using controlled deflection rolls, whichin certain instances may be of the nondeflecting type of swimming roll. The present invention thus provides an apparatus for controlling the calendering pressure exerted on a web passing sequentially through a series of pressure nips provided by a plurality of superposed calender rolls arranged in a single stack, including the step of regulating the downward load exerted on the adjacent lower roll by a controlled deflection roll located intermediately of the rolls, by regulating the forces acting on the supporting journals of the intennediate controlled deflection roll, whereby the nip pressures exerted by all the rolls located below the intermediate roll are correspondingly regulated. It will be understood by those skilled in the art that the fluid pressure within the controlled deflection roll is adjusted to provide the desired deflection condition of the roll for the related load condition. F

The apparatus for carrying out the present invention thus comprises a paper calendering roll stack having a plurality of substantially coplanar calender rolls in superposed relation including a controlled deflection roll located in an intermediate position of the stack, haw'ng support bearings at the ends thereof and roll-positioning means acting on the bearings to control the downward load imposed by the nondeflecting roll on the rolls positioned therebeneath, whereby the calendering nip premures of the stack may be controlled.

Embodiments of the present invention are described with reference to the accompanying drawings wherein FIG. 1 comprises a partial side view of a calendar stack according to the present invention; and

FIG. 2 is a view taken in the direction of the arrow A showing the end guide arrangement of the plain rolls of the stack.

Referring to FIG. 1 the calender stack 10 has a bottom roll 12 rotatably mounted in a roll support stand 11. A plurality of plain rolls 14, 16, 22, 24 are mounted in substantial coplanar vertical relation above the lower roll 12, and an intermediate roll 18 of the nondeflecting or Kusters" swimming roll is mounted intermediate the roll stack. The rolls are maintained in vertical alignment by means of bearing guide ring 26 at each end of the stack in guiding relation with roll bearings 28.

The adjustable nondeflecting roll 18 is supported by bearings 30 secured to a support arm 32 at each end of the roll. The support arms 32 are pivotally mounted at 34 to a bracket 36 carried by a side frame 38 on which is mounted an actuator 40 pivotally connected at 42 to the support arm 32.

In the illustrated embodiment the actuator 40 is of the double-acting type, so that either upward or downward loading may be applied to the roll 18. ln the illustrated embodiment, the lower roll 12 is of the nondeflecting type also. However, a plain roll may prove suitable at this position for certain calendering operations.

In addition to the foregoing advantages the present invention has the following additional advantages. By positioning a nondeflecting roll intermediately of the stack of rolls rather than at the bottom of the stack as previously practiced, both sides of the roll form effective nips, thereby providing an additional useable nip. By providing a nondeflecting roll at a higher than normal position in the calender stack, the spanwise deflection loads operating upon the rolls located above the nondeflecting roll are diminished, so that the size of rolls, i.e. the roll diameter, may be reduced thus providing reduction in capital cost.

Owing to the increased flexibility provided by the present arrangement the necessity of providing a second roll stack is obviated, thus reducing the costs of the apparatus and the amount of space required to accommodate the calenders. The savings in capital cost, for a very large paper machine, by implementing the single stack calender of the present invention, include the obviating of a drive for the second half of the stack, the reduction of building size by an additional bay, and

a reduction in the cost of calender controls. It will be evident that in operation the reduced-threading requirement provided by a single stack affords a significant improvement in paper machine performance, due to the reduction in time required for rethreading the web.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a high-speed paper calender having a full stack of rolls of sufficient self-weight that in an unrelieved condition crushing is caused to a lower one of the nips on passage of a sheet therethrough, the improvement comprising intermediate load relief means having a nondeflecting roll rotatably mounted in end bearings, being located a sufficient distance from the top of the stack to provide a desired extent of stack load relief, to relieve the pressures at the nips located therebeneath to values less than that at which crushing occurs, means for applying upward relief force in at least partial supporting relation with said end bearings, and means to precisely control said upwardforce-applying means so as to control limiting nip pressure in the stack, while maintaining all of the nips substantially unbowed.

2. The roll stack as claimed in claim 1 wherein said controlled roll is a swimming roll.

3. The roll stack as claimed in claim 1, wherein said control means for said controlled roll include support-bearing positioning means, whereby the load transfer to rolls positioned therebeneath may be controlled.

4. The roll stack as claimed in claim 1 wherein the lowermost one of said rolls is a nondeflecting roll. 

1. In a high-speed paper calender having a full stack of rolls of sufficient self-weight that in an unrelieved condition crushing is caused to a lower one of the nips on passage of a sheet therethrough, the improvement comprising intermediate load relief means having a nondeflecting roll rotatably mounted in end bearings, being located a sufficient distance from the top of the stack to provide a desired extent of stack load relief, to relieve the pressures at the nips located therebeneath to values less than that at which crushing occurs, means for applying upward relief force in at least partial supporting relation with said end bearings, and means to precisely control said upwardforce-applying means so as to control limiting nip pressure in the stack, while maintaining all of the nips substantially unbowed.
 2. The roll stack as claimed in claim 1 wherein said controlled roll is a swimming roll.
 3. The roll stack as claimed in claim 1, wherein said control means for said controlled roll include support-bearing positioning means, whereby the load transfer to rolls positioned therebeneath may be controlled.
 4. The roll stack as claimed in claim 1 wherein the lowermost one of said rolls is a nondeflecting roll. 